> So do humans, babies and the elderly especially.
Only the healthy adult form is taken into account generally, you wouldn't say that dragonflies are mainly swimming animals for example, even if they do spend most of their life underwater as larvae.
The point here is that kangaroos that are capable of bipedal motion will always choose quadrupedal motion at low speeds. While humans who can walk will always choose to walk when possible.
Yes we do, e.g. there's a sweet spot when scaling an incline (especially if there's easy handholds, e.g. a grassy incline) where using all fours is much easier and natural than making the same trips on two legs, even though you'd be perfectly capable of doing that too (i.e. I'm not talking about proper wall climbing).
Like it or not it's been a definitive example of a classic riddle since before it appeared in Oedipus Rex, an Athenian tragedy by Sophocles that was first performed c. 429 BC.
Only the healthy adult form is taken into account generally, you wouldn't say that dragonflies are mainly swimming animals for example, even if they do spend most of their life underwater as larvae.
The point here is that kangaroos that are capable of bipedal motion will always choose quadrupedal motion at low speeds. While humans who can walk will always choose to walk when possible.